The invention relates to a process for regenerating a cryopump operated with a refrigeration unit and including an inlet valve, cold surfaces which, during operation of the pump, have a temperature that causes gases to condense and which are heated for the purpose of regenerating them, the cryopump further including a backing pump that is connected with the interior of the pump by way of a valve. The invention also relates to a cryopump suitable for the implementation of this process.
A cryopump operated with a cold source or refrigeration unit is disclosed, for example, in DE-OS [Unexamined Published German Patent Application] 2,620,880. Pumps of this type are usually equipped with three cold surface regions which are intended for the accumulation of different types of gases. The first surface region is in a good thermally conducting contact with the first stage of the refrigeration unit and, depending on the type and power of the refrigeration unit, has an essentially constant temperature between 60 and 100 K. Usually a radiation shield and a baffle are associated with these surface regions. These components protect the lower temperature cold surfaces against incoming thermal radiation. The cold surfaces of the first stage preferably serve for the accumulation of relatively easily condensed gases, such as water vapor and carbon dioxide, by cryocondensation.
The second cold surface region is in thermally conducting contact with the second stage of the refrigeration unit. During operation of the pump, this stage has a temperature of about 20 K. The second surface region serves preferably for the removal of gases that are condensible only at lower temperatures, such as nitrogen, argon or the like, again by cryocondensation.
The third cold surface region also has the temperature of the second stage of the refrigeration unit (correspondingly lower if the refrigeration unit has three stages) and is covered with an adsorption material. These cold surfaces are provided essentially for the cryosorption of light gases, such as hydrogen, helium or the like.
For the regeneration of a cryopump it is necessary to heat the cold surfaces. This can be done by radiation or with the aid of heated regeneration gases that flow through the cryopump housing. Another possibility (see DE-OS 3,512,616) is to equip the cold surfaces with electrical heating devices and to operate the latter during the regeneration process. With the backing pump running and connected to the pump interior, the heating devices heat the cold surfaces, for example, to 70.degree. C. until, after the removal of the precipitated gases, the fore-vacuum pressure (about 10.sup.-2 mbar) is reached again in the pump interior. A total regeneration of the pump operated according to these methods takes many hours, particularly since the regeneration period is composed of the actual regeneration time and the time required to put the pump back into operation, particularly for cooling down the cold surfaces.
Cryopumps are frequently used in the production of semiconductors. In many applications of this type, most of the developing gases charge only the cold surfaces of the second stage. It is therefore known (see, for example, DE-OS 3,512,614) to regenerate only the low temperature cold surfaces. This is done by separately heating the cold surfaces of the second stage.
In all regeneration processes, the inlet valve usually preceding the inlet port of the cryopump must be closed, that is, pump operation and thus production operations must be interrupted.